The present invention relates to motor vehicle seats with a seat portion whose front edge can be raised, and a back rest whose upright position can be adjusted. This invention has particular application to automobile back seats, but may be used with other motor vehicle seats if desired.
U.K. patent application No. 2,300,352 discloses a motor vehicle seat in which the back rest pivots around a horizontal pivot tilt at the lower end of the back rest. The angle of pivot is determined by a clutch device, arranged in the upper region of the seat back, that makes it possible to lock the back rest in two different positions relative to the automobile car body. The back rest can also be decoupled from the car body and folded forward in order to provide increased cargo area in the trunk. When the angle of the back rest is changed, the seat portion is not adjusted, so that the available surface area of the seat portion changes depending on the tilt of the back rest. This means that, when the back rest is tilted, the position where the passenger""s hip joint should be located in the seat moves in both the horizontal and vertical directions, requiring that passengers reposition themselves.
French patent publication No. 2,750,085 discloses a motor vehicle seat whose seat portion is guided in the longitudinal direction along a curved guide that is fixed relative to the car body. The back rest is split such that, by means of a lever bar, which is moved together with the entire seat, the upper portion of the back rest is swiveled as the seat is moved longitudinally, so that the curvature of the back rest is changed. When the back rest tilt of the entire seat back changes, the hip joint location moves as well.
German patent publication No. DE 196 17 401 discloses a motor vehicle seat having a seat frame and seat cushion. The seat portion has a tilt adjustment mechanism which allows the seat portion to be inclined in such a way that the hip joint location changes by only a small amount. For this purpose, the seat cushion is coupled to the seat frame in such a way that the swivel axis of the tilt-adjustable seat portion is located beneath the hip joint location, at the shortest possible distance from it. However, as in other prior art mechanisms, the hip joint location moves when the back rest is tilted.
An adjustment device in which the angle of the back rest can be continuously adjusted, relative to the seat portion, is disclosed in U.S. Pat. No. 4,668,013. Two hinge portions, one of which is attached to the seat portion and the other of which is attached to the back rest, are connected through a planetary gear train. More particularly, one hinge portion has a pair of coaxial sun gears, i.e., gears with internally facing gear teeth, of differing diameters. The other hinge portion has a corresponding pair of planet gears, i.e., gears with externally facing gear teeth. Each planet gear has a slightly smaller outer diameter, and one less gear tooth, than the corresponding sun gear. The planet gears are eccentrically mounted relative to the sun gears on a common crank, so that the upon rotation of the crank, which is done by rotating an adjustment knob, the planet gears move in an orbital path relative to the sun gears. Due to the fact that each planet gear has one less gear tooth than the corresponding sun gear, the orbital motion of the planet gears, caused by rotating the knob, causes a small amount of rotation between the two hinge portions, thereby changing the tilt angle of the back rest.
The present invention is a motor vehicle seat having a back rest whose tilt angle can be adjusted in such a way that the hip joint location remains substantially unchanged. The seat portion may also be tilted, by raising its front edge, independently of the back rest tilt adjustment.
More particularly, a motor vehicle seat according to the invention includes a seat frame which is pivotably coupled to a back rest. A tilt adjustment device has a first hinge portion secured to the back rest and a second hinge portion rigidly connected to the car body for tilting the back rest about a horizontal tilt axis. The tilt adjustment mechanism is located at a height greater than the horizontal pivot connecting the back rest to the seat frame. The forward end of the seat frame is coupled to the car body such that the height and longitudinal position of the seat frame forward end are adjustable. Also, the horizontal pivot of the back rest is adjustable in height and longitudinal position. In this manner, when the back rest is tilted, the seat portion is moved forward or back so that the hip joint location of the passenger, relative to the seat portion, remains substantially unchanged.
Preferably, the forward end of the seat frame is coupled to a support region that is fixed relative to the car body by an adjustable length connecting linkage, so that the tilt angle of the seat can be adjusted independent of the tilt mechanism for the back rest.
As a result of coupling the seat portion to the back rest, the exposed seat area remains unchanged relative to the body of the user when the back rest is adjusted. The position of the passenger""s back also remains unchanged relative to the back rest, as the back rest is tilted, so that the back rest continues to support the back properly.
In one embodiment, all of the seat elements are arranged on a base frame, such that the seat is a modular unit which can easily be installed in a car body. A subframe may also be employed, which permits horizontal and vertical adjustment movement of the seat frame to be separated so that it is possible to compensate fully, or at least substantially, for the shift in the hip joint location caused by adjustment of the back rest. Adjustment of the seat tilt is possible independent of this compensation.
Adjustment of seat tilt is accomplished by means of a swivelling lever mechanism located at a forward region of the seat portion. The swivelling lever mechanism is designed with two lever members, and a rotational adjustment mechanism is inserted between the two levers. Adjustment of the seat tilt can alternately be achieved by means of a single, adjustable length swivelling lever.
For a better understanding of the invention, reference is made to the following detailed description of a preferred embodiment, taken in conjunction with the drawings accompanying the application.